1. Field of the Invention
The present invention relates to a monoclonal antibody which identifies the human blood group Fyab of the Duffy system and the use of such monoclonal antibody to provide protection against P. vivax malaria infection by eliciting anti-idiotypic antibodies.
2. Background Information
Malaria is the most prevalent infectious disease of mankind. Its widespread geographic distribution together with the severe pathologic consequences of the infection make malaria a major medical and financial burden for many of the developing nations.
Its enormous prevalence and the clinical severity of is effects underlie its biological consequences as a natural selection agent. It has been shown that the frequency of the sickle-cell trait increases in areas of high malarial endemia, owing to the resistance of red cells from Ss heterozygous individuals against the successful multiplication of intracellular forms of the malarial parasite (A. C. Allison, "Polymorphism and Natural Selection in Human Populations", Cold Spring Harbor Sympos., Quant. Biol., 29, 137, (1964)). This is true in spite of the gene frequency decrease caused by the invariably early lethality of the homozygous form of sickle cell disease in nature (Allison, supra and M. J. Friedman, "Oxidant Damage Mediates Variant Red Cell Resistance to Malaria", Nature, 280, 245, (1979)).
There are several different kinds of malaria, one of which is caused by the parasite P. vivax, which attacks the red blood cells of susceptible individuals. A genetic trait of special interest with regard to P. vivax is the absence of antigens encoded by the blood group system called Duffy (F. B. Livingston, "The Duffy Blood Groups, Vivax Malaria and Malaria Sections in Human Populations: Review", Human Biol., 56, 413, (1984)). It has been shown that individuals whose red blood cells lack the product of the Duffy genes are not susceptible to the penetration of P. vivax owing to the fact that Duffy molecules serve as the receptor for the parasite (L. H. Miller, H. J. Mason, D. F. Clyde and M. H. McGinnis, "The Resistance Factor to Plasmodium Vivax in Blacks, The Duffy Blood Group Genotype (a-b-)", N. Engl. J. Med., 295, 302, (1976)).
The sporozoan protozoa of the genus Plasmodium are pigment-producing ameboid intracellular parasites of vertebrates, with one habitat in red blood cells and another in cells of other tissues. There are at least five species of plasmodia that may infect humans, one of which is Plasmodium vivax ("P. vivax").
Malarial parasites are transmitted from host to host by blood sucking females of several species of the genus Anopheles. It is in the mosquito that the sexual phase of the life cycle of P. vivax takes place leading to the production of sporozoites. After their introduction into a "new" host, these sporozoites reside in the parenchymal cells of the liver and multiply asexually causing the eventual rupture of the hepatic cells and the release of the asexual forms (merozoites) into the blood stream. There they actively penetrate into red blood cells in a nearly synchronous fashion and because the rate of growth and cell division of P. vivax merozoites is essentially identical, the infected erythrocytes simultaneously reach the stage of parasite load at which they break. This produces the typical cycles of fever every 48 hours, hence the name of Tertian malaria.
P. vivax infection may persist without treatment for as long as five years. P. vivax parasitemias are relatively low-grade, primarily because the parasites favor either young or old red blood cells, but not both.
Immunity to P. vivax is commonly only partial in nature, which allows the occurrence of super infections that evolve independently causing an overlap in the cycles of parasite release leading to the appearance of fever in shorter cycles. P. vivax exhibits considerable antigenic "diversity" and "variation", as do other malarial Plasmodia (M. Hommel, "Antigenic Variation in Malaria Parasites", Immunology Today, 6, 28, (1985)), although it has been recently shown that antigenic components of P. vivax sporozoites exist that are common to parasites from different isolates (F. Zavala, A. Masuda, P. M. Graves, V. Nussenzweig and R. Nussenzweig, "Ubiquity of the Repetitive Epitope of the CS Protein in Different Isolates of Human Malaria Parasites", J. Immunol , 135, 2790, (1985)).
"Diversity" refers to phenotypic differences between different isolates of the same species and is accompanied by isolate-specific differences in neoantigens appearing on the surface of infected erythrocytes (M. Hommel, P. H. David and L. D. Oligino, "Surface Alterations of Erythrocytes in Plasmodium falciparum Malaria. I. Antigenic Variation, Antigenic Diversity and the Role of the Spleen", J. Exp. Med., 157, 1137, (1983)). There is evidence that the weak and temporary immunity exhibited by malaria patients, formerly called "premunition", is due at least in part to these parasite-dependent erythrocitic antigens, which are also specific to the parasite strain in question (M. Hommel, "Antigenic Variation in Malaria parasites", supra). Diversity is an obvious obstacle in the quest for effective immunogenic methods for human vaccination.
Antigenic "variation" is a further difficulty which refers to the capacity of a single organism to express sequentially a variety of antigens of different specificities. Thus, the Plasmodium population parasitizing a given individual may "switch" the antigens it expresses. Variation has been very well studied in, among other species, experimental P. knowlesi malaria in monkeys. For example, two cloned variants were shown to cause the emergence of two red blood cell membrane proteins, each which differed immunologically and even in molecular size (R. J. Howard, J. W. Barnwell and V. Kao, "Antigenic Variation in Plasmodium Knowlesi Malaria: Identification of the Variant Antigen on Infected Erythrocytes", Proc. Natl. Acad. Sci., USA, 80, 4129, . (1983)).
In the context of these sources of antigenic differences between P. vivax isolates and their consequences with regard to vaccination, it is important that the merozoites of different strains of P. vivax share the same receptor for penetration into red blood cells, i.e., the Duffy molecule (Miller et al, N. Engl. J. Med., supra). In addition, regardless of its capacity to vary other antigenic molecules, the parasite recognition molecule, i.e., the molecule that binds to the Duffy molecule, must remain constant since it is the complementarity between it and the invariant receptor that allows the penetration of merozoites into erythrocytes and thus, the continuity of the infection. Changes in the ligand specificity of this molecule would result in the loss of the parasite's capacity to infect, since P. vivax merozoites appear to be unable to utilize other human red blood cell receptors for their penetration in vivo, as shown by the resistance of Duffy negative erythrocytes.
If antibodies against the parasite's ligand could be induced in susceptible individuals, such antibodies would recognize the ligand on the surface of the merozoites and would block its capacity to interact with red blood cells. They might also result in a reaction similar to that caused by antibodies to the so-called circunsporozoite (CS) protein, which terminates in the destruction of the sporozoites's viability in vitro as described by R. S. Nussenzweig and V. Nussenzweig, "Development of Sporozoite Vaccines", Philos. Trans. R. Soc. Lond (Biol), 307, 117 (1984) and D. R. Spriggs, "The Malaria Sporozoite Vaccine: Parasitology's Brave New World", J. Infect. Dis., 152, 655, (1985). It has not been possible, thus far, to identify, characterize and prepare such ligand molecules to allow a test of this hypothesis.
Blocking of P. vivax penetration by conventional antibodies of the Duffy blood group was described by H. C. Spencer, L. H. Miller, W. E. Collins et al, "The Duffy Blood Group and Resistance to Plasmodium Vivax in Honduras", Am. J. Trop. Med. Hyg., 27, 664, (1978).